In the manufacture of automotive vehicles such as passenger cars and trucks, there are many safety standards that must be met by the vehicle to reduce the likelihood and/or severity of injury to occupants during an accident.
For example, in the United States, the safety standard FMVSS/208 deals with occupant crash protection during a frontal crash. In order to meet the safety standard, portions of an instrument panel assembly are required to absorb at least some of the energy of an impact by the knees of the driver during a crash. A portion of the instrument panel that is configured to sustain an impact from the knees of a driver during a crash is called a bolster. This is the portion of the instrument panel below the belt line.
Government tests are conducted on vehicles to determine if they meet the safety standard, based on the statistically median-sized male occupant. The median-size is a statistically determined size whereby 50% of the population is larger and 50% of the population is smaller.
Vehicle safety standards also require special design parameters relating to the steering column of the vehicle. The steering column must be designed to move in an axial direction if the chest of the driver contacts the steering wheel in the course of a crash. Most steering columns are designed to collapse in an axial direction and the steering column is located and designed with the collapsing structure being calculated on the basis that the steering column is not impacted by other structures within the vehicle. A further aspect of the impact safety design of the vehicle is that the driver's knees will contact the bolster area with one knee on either lateral side of the axis of the steering column. As the driver's knees contact the bolster area, the bolster may bend about a generally vertical plane. Bending of the bolster about a vertical plane may then result in some of the instrument panel structure, including the bolster itself, infringing on the space envelope allowed for the steering column structure. If there is any contact of this surrounding structure with the steering column, then the collapse characteristics of the steering column, in accordance with its design, will be changed due to contact from surrounding structure.
In order to deal with this problem, it is routine in automotive design to include a relatively strong structure, typically a metallic plate, which is attached to the instrument panel structure and which surrounds the steering column envelope. The metal plate may be attached to the bolster or to underlying instrument panel structure. The metal plate is more properly called a steering column protector and is sometimes referred to colloquially as a knee splitter. The function of the structure is to keep the driver's knees spread apart so that neither the knees, the bolster nor any other surrounding structure infringes on the steering column envelope. This ensures that the steering column can collapse in accordance with its designed function.
Most vehicles today have structure built in to help absorb the energy generated by the impact of the driver's knees on the bolster. Typically most vehicles have energy absorption brackets mounted laterally to either side of the steering column axis outside the steering column envelope. Energy is dissipated as the driver's knees contact the bolster pushing the bolster against the energy absorption brackets and some energy is dissipated by the energy absorption bracket. The energy absorption brackets are located to provide protection to the median sized person as constrained by the vehicle geometry.
In the existing design envelope, bolsters applied to the steering wheel area of cars are relatively complicated structures comprising a bolster as well as the steering column protector. The bolster generally is a surface of the instrument panel that would otherwise be available for viewing by a vehicle occupant and thus the bolster area must meet certain appearance characteristics. Heretofore, bolsters have been made from injection-molded parts, which have good appearance characteristics on the surface which is visible within the vehicle. However, due to the very nature of injection molding, parts made by the injection molding process often have less strength that might otherwise be available from the plastic resins used in the injection molding process. In such designs, an injection-molded bolster is created which has suitable appearance characteristics and the bolster is strengthened by a metallic plate. The steering column protector serves the function of protecting the steering column with the assumption that the driver's knees will be located substantially directly aft of the energy absorption brackets.
While this is a complicated and expensive structure to manufacture, there is also the question of what happens if the driver's knees are not located directly aft of the energy absorption structure. This may be as a result of the driver not meeting the 50 percentile adult male physical-size and the drivers seating position may locate the knees at some point other than directly aft of the energy absorption brackets.